Sub-band coding of speech includes dividing the speech spectrum into a plurality of frequency sub-bands, encoding the portions of the speech signal in the individual sub-bands and combining the encoded signals for transmission to a remote receiver. At the receiver the coded signals are decoded and reconstructed to generate the speech signal.
As described in an article entitled "Sub-band Coding With Adaptive Bit Allocation", Signal Processing, Vol. 2, No. 1, pp. 23-30, January 1980, a number of bits is allocated to each sub-band for the encoding of the portion of the speech spectrum in that sub-band based on a power estimate. The quality and efficiency of transmission of the encoded speech signals are enhanced by employing an adaptive bit allocation technique. However, information, commonly referred to as side information, must also be transmitted with the encoded speech signals in order to reconstruct the speech signal at the receiver. In the prior arrangement representations of power in each of the sub-bands are transmitted to a decoder for use in the speech reconstruction process. Transmission of the power representations for each sub-band requires use of significant transmission capacity. Additionally, bit allocation generation apparatus identical to that in the transmitter is required in the receiver to generate the bit allocation pattern corresponding to the encoded sub-band signals being received. Thus, transmission efficiency is diminished because of the need to transmit the power and receiver complexity is greater than desired.